1. Field of the Invention
The present invention relates to improved methods for the design of the various parts of a concept for building power-producing plants using the temperature difference between the warm surface waters of the tropical oceans, typically of the order of 27.degree. C. and the deep bottom waters which may approach the freezing point of salt water but generally are of a higher but useful temperature for condensing the steam bubbles produced. The general method of construction is to introduce the warm surface waters from a preferred depth below the surface, producing steam bubble nuclei, then forming steam bubbles of a desired size. These reduce the density of a rising column of seawater as in the old art of the air lift pump. The ALP, while functional, was poorly understood when this effort was undertaken. In the OTGHPP, The low--pressure steam filling the bubbles is condensed with the cold water pumped from lower ocean depths, the air released is eliminated and the resulting high density column of sea water is allowed to fall and exit through a suitably designed hydraulic turbine, producing shaftpower for driving a generator to produce electricity, or to drive other machines for on-site industrial uses. In its hydraulic aspects, the OTGHPP resembles the ALP, but thermodynamically the two concepts are dissimilar. The ALP requires power to produced compressed air to form the bubbles injected at its bottom, while the OTGHPP uses the heat of the warm ocean surface waters to produce voids in the form of steam bubbles.
2. Description of the Prior Art
The earliest known suggestion for producing power from the temperature difference in the tropical oceans between warm surface waters and deep cold water, producing the necessary temperature difference was by Lord Rayleigh in the late 19th century. He suggested evaporating a suitable working fluid to produce a high-pressure vapor which them would produce power in an engine or turbine of suitable design, and condensing the working fluid with the cold water in surface condensers. The best known and probably the first significant effort to produce a large, useful machine was by Georges Claude, a French inventor and successful developer of a method for liquifying air, which made his ocean efforts financially possible. Claude was probably one of the best informed of the industrialists at the time in using evaporating and condensing liquids in closed systems. He knew the difficulties and costs of transferring heat as suggested by Rayleigh, so avoided that path, opting for an open cycle leading to his 1935 patent. His method was simple but the equipment extremely large and costly. But he persevered, even to the point of commissioning his friend Rateau, the inventor of the impulse steam turbine, to design and build for him a low-pressure turbine specifically for use in his system. His problems were not entirely with the cycle chosen. He was overwhelmed with the sea-going problems because the state of the art in what has become to be known as "Ocean Engineering" was virtually nil. His equipment came to disasters at the hand of the oceans. The basic technical fault as I have analyzed his work lay in the fact that he produced very low pressure, high volume steam by throttling. The greater the throttling or constant energy pressure drop, the less the available pressure drop for the steam to use in the turbines. Low pressure (at about, for instance, a pressure of say, 0.05 bar) has such a low density and high specific volume(about 0.037 kg m.sup.-1 and 26 m.sup.3 kg.sup.-1 respectively) that it is virtually useless in practical turbines. Then, of course, to produce such low pressure steam by throttling uses most of the initial thermodynamic potential, which is marginal at best because of the relatively small temperature difference between warm surface waters and deep cold waters of the tropical oceans. Claude is known to have produced only a few papers, none specific in the thermodynamics and may never have realized the enormity of these thermodynamically limiting problems. But he did not give up easily.
There have been efforts to produce a system using the closed cycle, as suggested by Rayleigh, i.e. the reverse of a refrigeration cycle, wherein a working fluid such as ammonia is evaporated outside tubing heated by warm seawater flowing in the tubes, and condensing the vapor in a conventional surface condenser. The most ambitious and complete of these was a multi-year effort in the first half of the 1970's undertaken by the National Science Foundation and finally terminated in the same program after it was transferred to the Department of Energy. While this multi-pronged effort (it included work on many problems, from sea-keeping of floating systems, anchoring at sea, to transmission of power in bottom-laid cables to name a few) it did not produce a cost-effective design, All of this work is, of course, available to future system developers. A summary of this work would be very extensive, but here is how I view it in retrospect, as one of the many participants. The best possible system devised used massive tubes in great numbers, preferably made of titanium to provide long-life. But titanium, unlike copper-bearing alloys usually used in marine condensers, provides no protection against marine fouling. As an aside, the marine bronzes of use in condensing achieve a measure of anti-fouling only by wasting of toxic copper ions, so their life is short. Also, copper is not compatible chemically with ammonia, the probable working fluid (refrigerant) of choice. To top this picture off, realize that if a very large system using titanium tubes (which does not corrode in sea water) could be justified on the basis of the cost of power produced, only 1 plant capable of powering, say a city of 50,000 people could be built each year, if all the titanium produced were dedicated to that one plant. If we tried to produce all the power used in the United States with such plants, we'd need 5,000 years to build them, based on present production of titanium. Not an optimistic finding at best.
With that background, I describe briefly the thinking that led to my 1976 patent, and how it was deficient in detail and finally, how I have revised the OTGHPP's design to make up for those deficiencies. They were based largely on impressions from an extensive cavitation literature, and engineering handbook accounts of devices on which my concept was patterned in part, the air lift pump (ALP) and the Taylor hydraulic air compressor (THAC). First, a description of the ALP, one not found so far as I have been able to find in the scientific or engineering literature, even those that proposed to tell you how make one If you thrust an open vertical pipe part-way down in water, with its lower end at a depth below the surface, S (for submergence), that end is at a pressure equivalent to the static head of water at that depth. If you then (at considerable cost in power) introduce air bubbles at the lower end, and if they do not all coalesce (as they want to do, unfortunately) then you produce a low-density "foam". This foam is supported by the pressure equivalent to the submergence S, and rises in the pipe. At the top the air bubbles break and the water has been pumped to a height depending on the ratio of densities in the water and the foam columns density. The pumping effect produced is, of course, subject to the hydraulic laws as found in Bernoulli's equation. If the velocity is high, much of the available pressure, the product of S and density, .rho., is used in accelerating the foam mixture.
The THAC is, in effect, an upsidedown ALP. Visualize the pipe of the ALP raised until its lower end is just submerged, and water is then poured in at the upper end at a rate sufficient to keep it full. Then if you insert the open end of a tube into the upper end of the large tube carrying water downard (which preferably may be reduced cross sectional area in the nature of a venturi to lower the pressure and so induce air), air will be forced from the small tube into the down-flowing stream. A bubble will be carried down with the falling water and will feel increased pressure. The bubbles's contents will be compressed as the pressure in the water column rises with depth. At least one successful THAC was been built and used for producing compressed air for mining. Before being used, the volume of the air was increased by heating in a stove through which the pipe carrying it passed. Good thinking.
But this device, which promised to be of such value at the time of conception of the OTGHPP, proved to be unworkable as originally concieved. It was expected that the steam bubbles in the pump column of the steam lift pump (SLP) would be broken at its top, the steam condensed and the air released removed pretty much as envisioned in the engineering literature of the THAC. Unfortunately, my experiments in the late 1970's showed that both the THAC and barometric condenser which were part of the original concept would probably be impractical in this application. Further experiments on model ALP's and THAC's convinced me that the system would be impractical if (a) the steam bubbles were allowed to escape and (b) in breaking the steam (and of course, air) bubbles, the air released would require an impossibly large and efficient THAC. Also required would be a very large and tall barometric condenser. Such a condenser would let a lot of the water fall without making power.
The present invention describes the design changes in the OTGHPP necessary to nucleate, grow, and condense steam bubble and remove the air unavoidably released from large bubbles, although hopefully to be minimized in one of the several design features shown. Finally, much of the work done early in developing the instant improvements was to make a practical, large-scale OTGHPP capable of producing the prodigious amounts of power needed by modem industrial societies. Certainly the size of the tropical oceans is sufficient to produce the desired power if useful (cost, size, etc) power plants can be built and maintained at sea.
Patents are meant to be monopolies favoring the inventor during their life-times so not all trade secrets must be revealed. Nevertheless, I anticipate releasing much of my research work to assist rapid commercial development. The work is documented in a large number of monographs in my patent notebooks on Ocean Thermal Gradient Hydraulic Power Plant (File OTEC._) and Apparatus for Rapidly Degassing and Decontaminating Liquids (File DEGAS.---). Results reported in the later series resulted in a patent dated May 12, 1998, U.S. Pat. No. 5,749,945 to Beck, and referred to as Beck '98 from hereon, (hereby incorporated by reference). For simplicity in reading, I will avoid referring individually to these many monographs in preparing this patent application. But their existence may be implied with confidence by my readers. This application bears the file number OTEC.103 in the first of the two series.